The main differences between high-end cables are the materials used in the wires, in the plugs, and especially in any soldering. High end cable uses gold tipped plugs, thicker wires for better conductivity (less resistance), and a purer solder at the plug ends. Also, they are usually better shielded to help prevent RF interference, both in the cable and at the plug ends. If you want to go cheap, you can even use 2 strands of CAT-5 cable to carry the signal, just wire up your own plug ends.

My company sells professional multi-channel MPEG decoder circuit boards, and one of our products has 2 SPDIF connectors as 1/4 inch mini plugs on the board. Each connector carries the digital audio for 2 outputs of a 4 output board. Customers just need to wire up their own cable, or by an off-the-shelf cable that separates the 2 streams of 5.1 Dolby out of each wire. With that set up, one of our circuit boards can output 4 separate channels of high quality MPEG-2 video in either composite, S-video or RGB mode, and 4 separate Dolby 5.1 AC-3 streams via SPDIF connectors, or just plain old stereo in balanced or unbalanced connections.